There is considerable interest today in long haul optical transport networks. The most common optical transmission format for digital data in long haul applications is binary intensity modulation. In this format, a logical “1” corresponds to a pulse of light, while a logical “0” corresponds to the absence of a pulse. Light pulses are sent sequentially, at a pre-determined bit rate, where the bit period is the time duration between transmission of consecutive bits. For Non-Return-to-Zero (NRZ) transmission format, two consecutive “1”s are sent as a long pulse. In contrast, for Return-to-Zero (RZ) transmission format, each “1” corresponds to a single pulse, such that the intensity level returns to zero after each single pulse. In this transmission format, the pulse width must be smaller than the bit period. For long haul transmission, it is often advantageous to use the RZ format.
One common technique for transmitting RZ data is to optically generate a train of pulses, which are then “gated” by a data stream. The challenge associated with this approach is to properly synchronize the pulse stream with the data stream in a cost efficient manner. Past solutions, however, have generally failed in one respect or another. For instance, some solutions have included use of electrical frequency components, such as high bandwidth photodetectors and expensive RF filters. Other solutions have involved the use of driver taps and phase comparators calibrated at production, and do not adjust the actual relation as measured during use. While the first set of solutions are not cost-efficient, the latter solutions still allow for some unaccounted phase variation. Therefore, it is desirable to provide an improved method for synchronizing a pulse stream with a data stream in an optical communication system.